Lesson Plan - Get It!
Imagine yourself living in this beautiful house with windows and doors. The windows allow some natural light to get in, and the doors are used to get in and out of the house.
- But what if we remove the windows and doors, leaving your house with just walls and a roof?
It sounds crazy, indeed! Without windows or doors, you cannot control what goes in and out.
You can open windows to let in some sunlight or close them to keep bugs from entering the house. You can open and close doors to enter and leave the house.
Windows and doors also provide much-needed security, allowing you to stay warm and safe from intruders.
This example is no different than how cells prevent and allow substances to enter and leave through their cell membranes.
- How do cells facilitate transport?
Let's find out!
What Is Cell Transport?
Cell transport is the movement of substances across the cell membrane either into or out of the cell.
In a house, the walls serve as the membrane. We control who goes in and out through passages such as windows and doors. We can choose not to let a substance in or out by opening or closing these passages.
There are also two ways in which a cell can facilitate transport -- passive transport and active transport.
Before you delve deeper into the lesson, it is important that you review the following vocabulary words:
- solute - the substance that is being dissolved
- examples: salt, sugar, starch
- solvent - the substance that dissolves a solute
- examples: water, milk, ethanol
- solution - the homogeneous mixture of two or more substances
- examples: salt solution, sugar solution, starch solution
- concentration - the amount of solute in the solution
- example: high concentration is a high amount of solute in a solvent
Now that you understand these words, you may begin learning about the first type of cell transport.
Passive Transport and Active Transport
The cell membrane controls the entry of substances in and out of the cell. The direction in which substances travel is defined by two types of transport: passive and active.
The direction is determined by the way in which substances move to and from either a point of higher concentration or a point of lower concentration.
If you put more sugar (solute) in water (solvent), the sugar solution has a higher concentration. Likewise, if you just sprinkle a pinch of sugar over the same amount of water, the water becomes less concentrated.
A semi-permeable membrane can only allow certain molecules to pass through. Therefore, the membrane has an important job to do -- a gatekeeper!
Imagine riding a bike downhill.
- Do you need to pedal and exert effort?
The answer is no. The natural tendency of the bicycle is to move downward; therefore, no energy is needed.
Substances in passive transport do not need energy from the cell to move because their natural tendency is to go from a point of higher concentration to the point of lower concentration.
Now, imagine riding a bike uphill.
- Do you need to pedal and exert effort?
The answer is yes. The natural tendency of the bicycle is to move downward; therefore, energy is needed. You need to pedal harder!
Substances in active transport need energy from the cell to allow them to move from a point of lower concentration to a point of higher concentration. This is against their natural tendency; therefore, the cell requires energy to transport substances across the membrane.
To explore cell transportation further, check out the video below or read Defining Active and Passive Transport, by Anne Marie Helmenstine, Ph.D. for ThoughtCo.
Cell Transportation-Passive and Active Transport from MooMooMath and Science:
When you enter the house and smell your favorite dish or walk past someone and smell perfume, these are caused by a process called diffusion.
Diffusion is a type of passive transport where molecules spread from an area of higher concentration to an area of lower concentration.
Take a look at the model below!
The diagram shows how the particles are initially concentrated on a corner before slowly spreading out throughout the material.
When the particles are equally distributed in the material, a state of equilibrium is achieved. This means that the particles will no longer move around.
Review with What is diffusion? from BBC Bitesize. You can even try the quiz at the end to test your knowledge!
After learning about cell transportation and the difference between passive and active transport, it is time to move on to the Got It? section!